Mercury biomagnification in marine environments can result in toxicity to organisms at high trophic levels and impacts to cultural and economic activities (e.g., fishing) due to exceedances of safe mercury tissue concentrations. The risk of these impacts must be assessed by industries releasing mercury to the environment, such as the oil and gas industry in some decommissioning activities. This has resulted in the question to scientists: ‘how much mercury is safe to release to the marine environment?’.
Mercury biomagnification is dependent on a pipeline of mercury speciation changes, methylation, bioaccumulation, and transfer up trophic levels. A recent attempt to model biomagnification found that this assessment pipeline had large data gaps. Nonetheless, conservative estimates determined that mercury releases equivalent to the default ANZG (2018) water quality guideline for 99% species protection of 0.1 µg/L would increase organism tissue concentrations by less than 20%. This may be considered a ceiling of the true value and serves as a useful starting point for research prioritisation.
The key limitations of this approach are discussed in this presentation and include the lack of data linking the mass of mercury released to mercury available for methylation, rates of the inputs and exports of methylmercury to food webs, transfer of mercury between organisms within a food web.